GSM KPI Optimization Appendix3

ALUMS OMP L2 014 ALUMS 014 ALUMS OPERATIONAL PROCESS MANUAL ‐

EDITION 1.2 EDITION 1.2

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EFFECTIVE DATE: EFFECTIVE DATE: 01January 2011

KPI Optimization Process Appendix‐3 refers to page 15 of Network Performance Monitoring & Optimization Process

Huwaei



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PROCESS for SDCCH Assignment Success Rate Optimization: Definition:

When From the MS SDCCH Request is sent to Base Station and if MS

successfully gets the SDCCH in response SDCCH Assignment has done successfully.

PROCESS for Optimization: 1. Identify the Bad performing Cells for SDCCH Assignment Success Rate 2. Take the detailed report showing (Ex. Total SDCCH Assignment Request, Total SDCCH Assignment Successful) 3. Follow the below mentioned Process after Analyzing detailed report... 4. From Report Check whether you have Idle SDCCH available in cell or not for SDCCH Assignment; because the Main factor for lowering SDCCH Assignment success rate is SDCCH congestion. 5. SDCCH Congestion: a. Check The SDCCH Requests (Immediate Assignment Measurement Per Cell Report form M200) b. Ex. Call purpose, SMS, Location Update c. If you find High SDCCH Request and low TCH utilization Check “SDCCH Dynamic Allocation Allow” feature Allow” feature is enabled or not? if not enable this feature. d. If you have very High SDCCH Request for Location Updating; optimize the LAC boundary. e. Only For some exceptional cases you can increase the Static SDCCH Time Slots. 6. Check Hardware/Transmission alarms; Resolve if find any. 7. Audit for any parameters related discrepancies and define as per standard parameters set. 8. RF and Environmental Factors: a. Low Coverage Areas (Try to reduce low coverage patches with physical optimization; New sites) b. Interference/ Bad quality/ UL-DL Imbalance; c. Check the states for TRx on which SDCCH is configured can be issue of TRx also; Change TRx if you found random behavior of TRx. 9. After all rectification observe the subsequent days report if you still find the problem repeat the same process with due care to Pin Point the actual cause.



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PROCESS for SDCCH Assignment Success Rate Optimization: Definition:

When From the MS SDCCH Request is sent to Base Station and if MS

successfully gets the SDCCH in response SDCCH Assignment has done successfully.

PROCESS for Optimization: 1. Identify the Bad performing Cells for SDCCH Assignment Success Rate 2. Take the detailed report showing (Ex. Total SDCCH Assignment Request, Total SDCCH Assignment Successful) 3. Follow the below mentioned Process after Analyzing detailed report... 4. From Report Check whether you have Idle SDCCH available in cell or not for SDCCH Assignment; because the Main factor for lowering SDCCH Assignment success rate is SDCCH congestion. 5. SDCCH Congestion: a. Check The SDCCH Requests (Immediate Assignment Measurement Per Cell Report form M200) b. Ex. Call purpose, SMS, Location Update c. If you find High SDCCH Request and low TCH utilization Check “SDCCH Dynamic Allocation Allow” feature Allow” feature is enabled or not? if not enable this feature. d. If you have very High SDCCH Request for Location Updating; optimize the LAC boundary. e. Only For some exceptional cases you can increase the Static SDCCH Time Slots. 6. Check Hardware/Transmission alarms; Resolve if find any. 7. Audit for any parameters related discrepancies and define as per standard parameters set. 8. RF and Environmental Factors: a. Low Coverage Areas (Try to reduce low coverage patches with physical optimization; New sites) b. Interference/ Bad quality/ UL-DL Imbalance; c. Check the states for TRx on which SDCCH is configured can be issue of TRx also; Change TRx if you found random behavior of TRx. 9. After all rectification observe the subsequent days report if you still find the problem repeat the same process with due care to Pin Point the actual cause.



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Fish bone diagram for the root cause analysis high SDCCH congestion rate

PROCESS for SDCCH DROP Rate Optimization: Definition:

When MS is already on SDCCH and in-between communication with Base

station SDCCH channel got disconnected abruptly then SDCCH Drop has occurred.

PROCESS for Optimization: 1. Identify the Bad performing Cells for SDCCH Drop Rate 2. Take the detailed report showing (Ex. Total SDCCH Assignment Successful, Total SDCCH Dropped)



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3. Follow the below mentioned Process after Analyzing detailed report... 4. The Main Reasons for High SDCCH Drop Rate are improper Parameters Configuration and Bad RF & Environmental factors. 5. First Audit for any parameters related discrepancies and define as per standard parameters set. 6. Check for Neighbor Relations and correct if it is not proper. 7. For counter level analysis refer “Call “ Call Drop Measurement per Cell” Cell ” report from M2000. 8. Low Coverage: Through Drive Test Find out the low coverage patched and try to improve with physical optimization; New site; coverage enhancement features for some cases(Ex. cases( Ex. Power Boost Tech, No Combining, TMA/TMB) TMA/TMB ) 9. Interference: Check for interference from repeaters, Intra-Network interference due to aggressive reuse or improper Freq., Inter-Network can also be the case. Find out the actual cause and rectify it. 10. Antenna System: High VSWR due to feeders, Improper antenna configuration( Ex. Sector cable Swap) Swap) 11. Check for Hardware Issue and rectify if you found any. 12. After the activity check the subsequent days report and repeat the procedure for pin pointing the actual cause.

Fish bone diagram for the root cause analysis for high SDCCH drop rate



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PROCESS for RACH (Random Access Channel) Success Rate Optimization: Definition: Random Access Channel (RACH) is used by the MS on the “uplink” to request for allocation of an SDCCH. This request from the MS on the uplink could either be as a page response (MS being paged by the BSS in response to an incoming call) or due to user trying to access the network to establish a call. For all services there will CH REQ (Channel Request) from MS and in the response of CH REQ if MS will get the IMM ASS CMD (Signaling Ch) Access to system is successful. Nature of this Access REQ is random so it is call Random Access Channel Request.

PROCESS for Optimization: 1. Identify the Bad performing Cells for RACH Success Rate 2. Take detailed report and analyze for no of failure of Request and failures. 3. The main reasons for bad RACH success rate could be access from very distant place with very low coverage; Parameters Configuration discrepancies. 4. First Check for Parameters Configuration discrepancies and correct as per standard parameter set. 5. The main parameters to look for Huawei a. “MS MAX Retrans” Retrans” can set depending upon Traffic and Clutter. b. “Tx-Interger Tx-Interger”” will reduce the RACH collision and can improve RACH success rate. c. “T3122 T3122”” waiting time for next network access. d. “RACH Min.Access Level(dbm)” Level(dbm) ” very important parameter for low coverage rural areas. e. “CCCH conf” & “BS_AG_BLKS_RES” check properly defined or not? Because if you have overload with AGCH “IMM ASS” can’t be send in the response of CH REQ. 6. Check for Hardware Issues (Ex. ( Ex. BTS sensitivity has very crucial role to play here) 7. Check for Uplink Interference and quality. 8. Check for UL-DL imbalance and correct if any problem.

ALUMS OMP L2 014 ALUMS OPERATIONAL PROCESS MANUAL ‐

EDITION 1.2

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EFFECTIVE DATE: 01January 2011

9. After the activity check the subsequent days report and repeat the procedure for pin pointing the actual cause.

Fish Bone diagram for the root cause analysis of poor Random Access Success


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PROCESS for TCH Assignment Success Rate Optimization: Definition:

When From the MS TCH Request is sent to Base Station and if MS successfully

gets the TCH in response TCH Assignment has done successfully.

PROCESS for Optimization: 1. Identify the Bad performing Cells for TASR( TCH Assignment Success Rate) 2. Take the detailed report showing (Ex. Total Assignment Request, Total Assignment Successful) 3. Follow the below mentioned Process after Analyzing detailed report... 4. From Report Check whether you have Idle TCH available in cell or not for Assignment and follow the below process.


EDITION 1.2

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A & B in above Flow chart are measurement Points for TCH Assignment Failures...

5. As per the Above Process If you have already used “ Re-Assignment”, “ Directed Retry” and “Queuing” features and still you are having issue with TCH Congestion (No Idle TCH)... Try to Decrease Half Rate Triggering Thresholds... 6. Ex. Below Parameters for Huawei System “TCH Busy Traffic Threshold (%)” “AMR TCH/H Prior Allowed” “AMR TCH/H Prior Cell Load Threshold” 7. Check for discrepancies with Parameter Configuration and set as per Standard Parameters set available. 8. If you find Issue is not with High Traffic and Congestion... Check Hardware Issue (Ex. BTS/BSC/MSC hardware / UL-DL Imbalance due to VSWR) resolve if you find any. 9. Transmission Issues at A-bis/A-ter/A links 10. If Hardware is Ok check for Bad RF Environment... (Very low Coverage, High Interference, Bad Quality, Call from Distant Place (TA). 11. Follow below Process for Above Points... You can check the counters Report for Pin pointing the actual cause. (Ex. Assignment Per Cell Report from M2000)


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12. Correct the affected area (Ex. If call is getting originated from High TA and getting failed due improper strength ; Optimize the Site Coverage with Physical Optimization) and check the subsequent days Report; If you still find the issue follow the same flow right from the starting with due care to PIN Point the Actual cause.. 13. TBF Success Rate 14. Average GPRS RLC throughput & Average EDGE RLC Throughput 15. Downlink Multislot Assignment Success Rate 16. SDCCH Assignment Success Rate 17. SDCCH DROP Rate 18. ACH (Random Access Channel) Success Rate 19.

Assignment Success Rate


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PROCESS for Rx Quality Optimization: • •

Definition : Rx Quality is measure of BER of radio link

between MS and BTS

Poor Speech Quality could be due to •

Patchy Coverage ( holes)

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No Target cell for Handover

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Echo , Audio holes, Voice Clipping

Interference ---: •

Co-channel

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Adjacent channel

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External

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Multipath

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Noise

Speech Quality Parameters •

RxQUAL: Measured on the midamble.

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Indicates poor speech quality due to radio interface impairments

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FER : Measured on the basis of BFI ( Ping -Pong effect on speech )

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Preferred under Frequency Hopping situation

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Audio holes: Blank period of speech, due to malfunctioning of Transcoder boards or PCM circuits. Mean Opinion Score (MOS) : ITU standard for estimating speech quality

PROCESS for Optimization:


EDITION 1.2

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1) Physical optimization 2) New cell dependency 3) Overshooting 4) Neighbor list tuning 5) BCCH tuning (Freq plan)

ALUMS

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MP L2 014 AL MS OPERATIO NAL PROCESS ‐

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ANUAL

EFFECTI E DATE: 01Jan ary 2011

From M 000 extract Rx Quality measureme t distributi n Counters to know Tr –cell wise Rx Quality.


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PROCESS for HOSR Optimization: Definition: HO activity is performaed to maintain – Call continuity and

call quality . The

inputs that the BSC uses for making a handover decision, from the received MRs from the MS is the DL signal strength, DL quality, and the signal strength of the six best reported neighbours. From the serving BTS, for the same MS the BSC will use UL signal strength, UL quality and TA.

Handover Process: The GSM handover process uses a mobile assisted technique for accurate and fast handovers, in order to: - Maintain the user connection link quality. - Manage traffic distribution The overall handover process is implemented in the MS,BSS & MSC. Measurement of radio subsystem downlink performance and signal strengths received from surrounding cells, is made in the MS. These measurements are sent to the BSS for assessment. The BSS measures the uplink performance for the MS being served and also assesses the signal strength of interference on its idle traffic channels. Initial assessment of the measurements in conjunction with defined thresholds and handover strategy may be performed in the BSS. Assessment requiring measurement results from other BSS or other information resident in the MSC, may be perform. in the MSC. The MS assists the handover decision process by performing certain measurements. When the MS is engaged in a speech conversation, a portion of the TDMA frame is idle while the rest of the frame is used for uplink (BTS receive) and downlink (BTS transmit) timeslots.


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During the idle time period of the frame, the MS changes radio channel frequency and monitors and measures the signal level of the six best neighbor cells. Measurements which feed the handover decision algorithm are made at both ends of the radio link.

Classification By Reason: •

Emergency HO –

Timing advance (TA) Emergency HO

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Bad quality (BQ) Emergency HO

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Rx Level Drop Emergency HO

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Interference emergency HO

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load HO

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Normal HO

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Edge HO

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Layer HO

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Power budget (PBGT) HO

Fast moving MS HO (Speed-sensitive HO )

PROCESS for Optimization: 10. Identify the Bad performing Cells for HOSR 11. Take the detailed report showing cause & target cell 12. Check congestion; hardware Alarm; Quality; Rx level 13. Late Handover – Handover margin (like Rx level-Rx Qual etc )need to define properly. 14. Ping-Pong Handover – A proper Hysteresis is used to prevent the Ping Pong effect. This can be caused by fading 15. Unnecessary Handover – more number of handovers, higher risk of facing quality problem and even in call drop


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16. Missing neighbor – Best server is not in there in neighbor list 17. BCCH Missing 18. Same BCCH & BSIC combination 19. one way neighbor handover 20. Neighbor cell in other BSC- need to define correct CGI,BCCHNO,BSIC 21. Congestion on other cell

Fish bone diagram for the root cause analysis for high handover failure rate

PROCESS for TCH drop Optimization: Definition:

TCH drop (or a dropped call) could be broadly classified into 3 sub classes:

1. Degradation of the links (Uplink and Downlink): either degradation of Signal Strength which falls near or lower than the sensitivity of the base station (around to -110 dBm) or that of the mobile (around -104dBm) or degradation of quality of the links (Uplink and Downlink) often due to interference. 2. Excess TA (TA>63 or excess path imbalance due to high TA). 3. Other Reasons.


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PROCESS for Optimization: Call drops are identified through SACCH messages. A Radio Link Failure Counter value is broadcast on the BCH. The counter value may vary from network to network. At the establishment of a dedicated channel, the counter is set to the broadcast value (which will be the maximum allowable for the connection). The mobile decrements the counter by 1 for every FER (unrecoverable block of data) detected on the SACCH and increases the counter by 2 for every data block that is correctly received (up to the initial maximum value). If this counter reaches zero, a radio link failure is declared by the mobile and it returns back to the idle mode. If the counter reaches zero when the mobile is on a SDCCH then it is an SDCCH Drop. If it happens on a TCH, it is a TCH drop. Sometimes an attempted handover, which may in itself have been an attempt to prevent a drop, can result in a dropped call. When the quality drops, a mobile is usually commanded to perform a handover. Sometimes however, when it attempts to handover, it finds that the target cell is not suitable. When this happens it jumps back to the old cell and sends a Handover Failure message to the old cell. At this stage, if the handover was attempted at the survival threshold, the call may get dropped anyway. If on the other hand the thresholds were somewhat higher, the network can attempt another handover. 1

2

Channel Request

Channel R equest

Im m A s s i g n m e n t

Im m A s s i g n m e n t

S e rvic e R e q u e s t

S e rvic e R e q u e s t

S i g n a l li n g : S ig n a llin g

S D C C H

S i g n a l li n g : S peech

T C H

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RLT = 0 ; DRO P S

R LT = 0 ; DR O P S

S D C C H D R O P !

TC H D R O P !

SDC CH / TCH H a n d o ve r C o m m a n d Hand Access H a n d o v e r F a i lu r e

ALUMS

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EDITION 1.

MP L2 014 AL MS OPERATIO NAL PROCESS ‐

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ANUAL

EFFECTI E DATE: 01Jan ary 2011

From M 000 extract Call Drop

easurement counters t know cause.


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8.3.1 Fish bone diagram for the root cause analysis for high TCH Drop Rate E x t e r n a l I n te r f e r e n c e

L o w S ig n a l S tr e n g t h D L

L o w S ig n al S tr e n g t h U L

TCH Drop Rate

H i g h T A /R F S p i ll a g e /P a t h I m b a l e n c e

B a d Q u a li t y D L

B a d Q u a li t y U L

Figure 1: Fish bone diagram for the root cause analysis for high TCH Drop Rate

C LS

HCS

H a r dw a r e Fa u lt s

D r o ps d u e to O t h er R e a so n

TCH Drop Rate

Assignment to another cell

Handover Failures

P o w er C o nt ro l

Figure 2: Fish bone diagram for the root cause analysis for high TCH Drop Rate

S u dd e n Lo st C o nn ec ti on


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PROCESS for SCR: Definition:

SCR = ((Total Call - INTERNAL_FAILURES)/TOTAL CALLS) x 100%...

Total Call = BSS Originate Call->2G ORG CALL ATTEMPT TIMES + Trunk Office Direction Incoming Office Traffic->SEIZURE TIMES INTERNAL_FAILURES = Failure Reason Traffic-> CAUSE013_switch equipment congestion + CAUSE016_temporary failure + CAUSE027_switch equipment failure + CAUSE061_no CR resource + CAUSE062_no CCB resource + CAUSE166_network error + CAUSE169_temporary error + CAUSE170_device congestion + CAUSE201_IWF resource unavailable

PROCESS for Optimization:

1. Identify the Failure reasons count for each internal failure reason. 2. Check detailed explanation of cause values those contributing the major factor.


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PROCESS for Paging Success Rate: Definition: Paging Success rate is the percentage of valid page responses received by the system PSR = ( CC service first paging response number + CC service repeat paging response number+ SMS service first paging response number + SMS service repeat paging response number) / (CC service first send paging number + SMS service first send paging number)*100

PROCESS for Optimization: 1. Removal of non existing Cell site database created in BSCs 2. Correcting the number of LACs per BSC (Minimizing the number of LAC per BSC)


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3. Standard template of Cell site database in each BSC. 1 Fish bone diagram for the root cause analysis of poor Paging Success Rate 3 . In c o r r e c t M S C P a r a m e t e rs

1 . In c o r re c t C e l l P a r a m e t e r s

Poor Paging Succ R ate

5 . P o o r P a g in g S t ra t e g y

4 . P oo r R F

2 . E xc e s s p a g in g D is c a rd s

Figure 1 : Root Cause for Poor Paging Succ Rate (1)

10. ABIS , A interface fluctuations, Errors

8. incorrect LAC Dimension

6. SDCCH Congestion

Poor Paging Succ Rate

11. decrease signalling load on CCCH

9. ABIS , A interface Congestion 7. Combined BCCH

Figure 2 : Root Cause for Poor Paging Succ Rate (2)


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PROCESS for SS7 Signaling Load: Definition: 1. TRANSMITT LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING OCTETS TRANSMITTED + 6 *(MSU TRANSMITTED + MSU RETRANSMITTED) ) / (248000 * 3600 * 0.2) ) * 100) -----> HSL 2. TRANSMITT LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING OCTETSTRANSMITTED + 6 *(MSU TRANSMITTED + MSU RETRANSMITTED) ) / (8000 * 3600 * 0.4) ) * 100) -----> OTHER THAN HSL 3. RECEIVE LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING OCTETS RECEIVED + 6 *(MSU RECEIVED) ) / (248000 * 3600 * 0.2) ) * 100) -----> HSL 4. RECEIVE LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING OCTETS RECEIVED + 6 *(MSU RECEIVED) ) / (8000 * 3600 * 0.4) ) * 100) -----> OTHER THAN HSL

PROCESS for Optimization: 1. Identify the signaling links whose utilization is going above 80%. 2. Prepared Plan for additional signaling links as per requirement…


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PROCESS for TBF Success Rate Optimization:

Definition:

Temporary Block Flow (TBF) is a physical connection used by the two Radio

Resource entities to support the unidirectional transfer of PDUs on packet data physical channels. The TBF is allocated radio resource on one or more PDCHs and comprises a number of RLC/MAC blocks carrying one or more LLC PDU. TBF Success Rate is when during a data session, TBFs are successfully established on UL and DL.

PROCESS for Optimization: 22. Identify the Bad performing Cells for TBF Success Rate. 23. Identify the bifurcation of Poor TBF Success Rate: whether UL or DL is poor or it is poor in both directions. 24. Take the detailed report showing (Ex. Total TBF Requests, Total TBF Success, Failure reasons) 25. Identify the failure reasons after analyzing detailed report and follow the below mentioned process. Failure is mainly due to TBF Congestion or MS No response. 26. TBF Congestion: a. Check The Static and Dynamic PDCH definition from BSC Configuration data ) b. If you find Zero Static or Dynamic PDCH, define the same. c. If PDCH definition is sufficient as per the guidelines, then check whether the TBF requests are high. If requests are high, then we need to define more PDCHs in the cell. But before defining more PDCHs, check whether the Voice Utilization is not high and there is no TCH Congestion in the cell.. 27. Check Hardware/TRX alarms; Resolve if find any. 28. Audit for any parameters related discrepancies and define as per standard parameters set. 29. MS No Response: RF and Environmental Factors: a. Low Coverage Areas (Try to reduce low coverage patches with physical optimization; New sites) b. Interference/ Bad quality/ UL-DL Imbalance;


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c. Check the states for TRx on which PDCH is configured can be issue of TRx also; Change TRx if you found random behavior of TRx. After all rectification observe the subsequent days report if you still find the problem repeat the same process with due care to Pin Point the actual cause.

PROCESS for Optimization of Average GPRS RLC throughput and Average EDGE RLC Throughput: Definition:

Throughput is the amount of data uploaded/downloaded per unit of time.

PROCESS for Optimization: 1. Identify the Bad performing Cells for Poor GPRS/EDGE Throughput. 2. Identify the bifurcation of Poor Throughput: whether UL or DL is poor or it is poor in both directions. 3. Take the detailed report showing (Ex. Total TBF Requests, Coding Scheme Utilization) 4. Identify the cells after analyzing detailed report and follow the below mentioned process. 5. Take the configuration dump of the poor cells: a. Check The Static and Dynamic PDCH definition from BSC Configuration data ) b. If you find Zero Static or Dynamic PDCH, define the same. c. If PDCH definition is sufficient as per the guidelines, then check whether the TBF requests are high. If requests are high, then we need to define more PDCHs in the cell. But before defining more PDCHs, check whether the Voice Utilization is not high and there is no TCH Congestion in the cell. d. Check whether there are enough Idle TS defined at the site. If not, definition to be done. 6. Check whether it is due to poor radio conditions/interference; check C/I. Perform a drive test to analyze the cell in more detail. 7. Check Gb Congestion/Utilization at the BSC/PCU. 8. Check Hardware/TRX alarms; Resolve if find any. 9. Audit for any parameters related discrepancies and define as per standard parameters set.


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After all rectification observe the subsequent days report if you still find the problem repeat the same process with due care to Pin Point the actual cause.

PROCESS for Optimization of Downlink Multislot Assignment Success Rate: Definition:

User timeslot request based on traffic types and MS multi-timeslot capability

and the actual timeslot allocated by the system which can also be termed as Downlink Multislot Assignment Success rate .

PROCESS for Optimization: 1. Identify the Bad performing Cells for Poor DL Multislot Assignment. 2. Take the detailed report showing (Ex. Total TBF Requests, Failure in terms of TS requests) 3. Identify the cells after analyzing detailed report and follow the below mentioned process. 4. Take the configuration dump of the poor cells: a. Check The Static and Dynamic PDCH definition from BSC Configuration data ) b. If you find Zero Static or Dynamic PDCH, define the same. c. If PDCH definition is sufficient as per the guidelines, then check whether the TBF requests are high. If requests are high, then we need to define more PDCHs in the cell. But before defining more PDCHs, check whether the Voice Utilization is not high and there is no TCH Congestion in the cell. d. Check the multiplexing thresholds and upgrade/downgrade reports. 5. Check whether it is due to poor radio conditions/interference; check C/I. Perform a drive test to analyze the cell in more detail.


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6. Check Gb Congestion/PCU-DSP Utilization. 7. Check Hardware/TRX alarms; Resolve if find any. 8. Audit for any parameters related discrepancies and define as per standard parameters set. After all rectification observe the subsequent days report if you still find the problem repeat the same process with due care to Pin Point the actual cause.


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KPI Optimization Process Appendix‐3 (contd..) refers to page 15 of Network Performance Monitoring & Optimization Process

Alcatel & ZTE

The document covers the TCH Assignment Success rate & SDCCH Congestion optimization process for Alcatel & ZTE GSM Radio Networks to be complaint by Alcatel Lucent Managed Solutions India Pvt. Ltd Radio Optimization Engineers & associated staff. ‐


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Contents 1. PURPOSE………………………………………………………………………………………….4 2. SCOPE………………………………………………………………………………………………4 3. INTRODUCTION……………………………………………………………………………….4 4. DEFINITION……………………………………………………………………………………..5 4.1 TCH ASSIGNMENT SUCCESS RATE (TASR) 4.2 SDCCH CONGESTION (SD CONG)

5. VENDOR WISE COUNTER BASED DESCRIPTION 5.1 TCH ASSIGNMENT SUCCESS RATE (TASR) 5.1.1 ALCATEL TASR DESCRIPTION 5.1.2 ZTE TASR DESCRIPTION

5.2 SDCCH CONGESTION (SD CONG) 5.2.1 ALCATEL SD CONG DESCRIPTION 5.2.2 ZTE SD CONG DESCRIPTION

6. VENDOR WISE ROOT CAUSE ANALYSIS & OPTIMIZATION STEPS 6.1 TCH ASSIGNMENT SUCCESS RATE (TASR) 6.1.1 ALCATEL TASR ANALYSIS 6.1.2 ZTE TASR ANALYSIS


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6.2 SDCCH CONGESTION (SD CONG) 6.2.1 ALCATEL SD CONG ANALYSIS 6.2.2 ZTE SD CONG ANALYSIS

7. APPENDIX 7.1 SDCCH DIMENSIONING 7.1.1 ALCATEL SD DIMENSIONING METHOD 7.1.2 ZTE SD DIMENSIONING METHOD

8. Optimization Process for other Radio KPIs


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1. PURPOSE This document serves as a process guideline for key performance indicator (KPI) optimization such as TCH Assignment Success Rate (TASR) and SDCCH (SD) Congestion in advanced wireless GSM 2G networks in multi vendor scenario ‐

comprising of Alcatel (B10 version) & ZTE (ZXG10 2.97) Radio systems. ‐

2. SCOPE This document is meant for experienced wireless 2G GSM professionals involved in key performance indicator (KPI) optimization specifically TCH Assignment Success Rate (TASR) and SDCCH (SD) Congestion in multi vendor scenario comprising of ‐

Alcatel (B10 version) & ZTE (ZXG10 2.97) Radio systems. ‐

Also, the document targets the internal customers of ALUMS with sufficient background in GSM.

3. INTRODUCTION Dynamic network configuration changes, operation & maintenance activities with exponentially rising curve of subscriber density for wireless services prompts the radio engineers to be quick & effective to retain the Quality of Services (QoS) in current scenario. TCH Assignment Success Rate (TASR) and SDCCH congestion are two critical pointers to quality of network accessibility during busy hours & non busy hours for the subscribers. Ideally, cells in the network needs to be designed for 0% SDCCH congestion & 100% TASR to ensure 100 % error free subscriber services initiated from the MS to ‐

the MSC. Practically, the real time radio environment (changing clutters), high level of faults/outages in network elements (MSC/BSC/TRAU/BTS) and higher subscriber services (Voice/Data) demands destabilizes the designed network capacity to result in degradation of TASR & SDCCH congestion.


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In order to achieve sustainable demand, the network resources are re

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dimensioned periodically with coverage/capacity/KPI optimization as when required basis and TASR / SD Congestion stands prime focus area as to be discussed.

4. DEFINITION 4.1 TCH ASSIGNMENT SUCCESS RATE (TASR) In general, TASR is defined as percentage ratio of successful TCH Attempts to TCH Attempts over an observed period of time. It measures how often setup message sent from MS for Mobile Originating Call (MOC) or Mobile Terminating Call (MTC) is successful during TCH allocation procedure from MSC. General Equation:

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TASR (%) = (TCH Attempt seizures/TCH Attempts) *100 GSM Layer 3 Equation:

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TASR (%) = (No. of Assignment Complete msg. /Assign Requests.)*100 Figure 1 Successful TCH Assignment phase


EDITION 1.2

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TCH ASSIGN

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MENT PHASE

Although, TASR indicates successful TCH seizures for MS connectivity with the network during call phase. Better way to approach TASR improvement is to focus on TCH Assignment failure rate which is equally important. High TCH Assignment failures can be observed for under reasons: •

Hardware faults in Network elements (BTS/BSC/MSC)

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Software & Network configuration database discrepancy

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Low Coverage zone

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Path loss issue

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High Interference from internal/external sources

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Transmission issues in A bis/A ter links

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CIC mismatches between BSC MSC

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BTS wiring diagram issue

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Incorrect Feature, Parameters & Timer usages

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Mismatch in TRX radio timeslots mapping on RSL

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Sector blocking due to clutter issues

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TCH Congestion

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High Traffic Utilization

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•

Wrong antenna type deployments for required clutters

•

Invalid counter pegging

•

Incorrect counter selection for failure monitoring

TASR improvement based on above mentioned causes is covered in Vendor wise root cause analysis & Optimization steps section. Many internal system reports based on measurable counters are required to co correlate to ‐

arrive at certain conclusion for improvement action and are covered in up

‐

coming sections. Assignment failure cause points are shown in figure as under: Figure 2 TCH Assignment failure cause points

MS

BTS

BSC

Um

A bis ‐

TRAU A

MSC A ter ‐

Legend: Assignment failure cause point:

‐

4.2 SDCCH CONGESTION (SD CONG) In general, SDCCH Congestion is defined as the percentage ratio of SDCCH Blocks to total SDCCH Attempts over an observed period of time. It measures how often Mobile Station (MS) is unable to access the network for various signaling (MM/CC) procedures to ensure subscriber service establishment. General Equation:

‐

SD CONG (%) = (SD Blocks/SD Attempts) *100 GSM Layer 3 Equation:

‐

SD CONG (%) = (Immediate Assign. Rejects /Channel Required) *100 In case of SDCCH

Figure 3 SDCCH Assignment phase

Congestion,

IMMEDIATE ASSIGNMENT REJECT message flows from BTS to MS on AGCH


EDITION 1.2

‐

‐


SDCCH ASSIGN

‐

MENT PHASE

Various Mobility Management (MM) sub layer and Connection ‐

Management (CM) sub layer procedures require usage of SDCCH channel ‐

between MS and MSC. Some of the commonly observed signaling procedures on SDCCH are as under: •

Normal Location Update (LU)

•

Periodic Registration

•

IMSI Attach/Detach

•

Call Setup (MOC/MTC)

•

SMS point to point (MO/MT)

•

Fax Setup

•

Supplementary services (USSD)

Most of the root causes for SD Cong % are listed under: •

Improper SDCCH Dimensioning

•

Incorrect usage of available features, parameters & timers

•

High TCH Utilization

•

Non optimized LAC Borders (Inter cell/Inter BSC/Inter MSC)

•

Configured but out of service SDCCHs

•

Phantom RACHs (Co BCCH/BSIC )


‐

EDITION 1.2

‐


•

Overshooting cells inside the clutter

•

Equipment failure (Cell/TRE/BSC)

•

Increased mean hold time of SDCCH due to large no. of Layer 3 message flows between MS MSC ‐

•

LAPD congestion in A bis interface ‐

SDCCH Congestion cause points are shown in figure as under: Figure 4 SDCCH Congestion cause points

MS

BTS Um

BSC A bis ‐

TRAU A

MSC A ter ‐

Legend: SDCCH Congestion cause point:

‐

SDCCH Congestion cause points are the locations where probable event failures are observed due to various reasons mentioned above. SDCCH Congestion improvement based on above mentioned causes is covered in Vendor wise root cause analysis & Optimization steps section. Many internal system reports based on measurable counters are required to co

‐

correlate to arrive at certain conclusion for improvement action and are covered in up coming sections. ‐

5. VENDOR WISE COUNTER BASED DESCRIPTION 5.1 TCH ASSIGNMENT SUCCESS RATE (TASR)


‐

EDITION 1.2

‐


5.1.1 ALCATEL TASR DESCRIPTION Alcatel BSS system (B10) evaluates the TASR based on certain measurable counters from NPO with below relation: TASR (%) = MC718 / [MC140a (MC142e+MC142f)*100. ‐

Also, MC142e=C142a+C142c & MC142f=C142b+C142d. Counters increment or decrement based on various factors governing the network operator settings and real time operational status. It is important to be aware of TASR % value on cell basis to visualize the impact & validity of these counters.

5.1.2 ZTE TASR DESCRIPTION ZTE BSS system (ZXG10 V2.97) evaluates the TASR based on certain ‐

measurable counters from OMCR with below relation: TASR

%

=

{(C11609 C11696) ‐

‐

(C11610+C11654+C11658 C11697 ‐

‐

C116101 C116133)} * 100 / (C11609 C11696) ‐

‐

Counter description & details can be found in Appendix section or on click to respective counter in quicker way.

5.2 SDCCH CONGESTION (SD CONG) 5.2.1 ALCATEL SD CONG DESCRIPTION Alcatel BSS system (B10) evaluates the SD CONG based on certain measurable counters from NPO with below relation: SD CONG (%) = [MC04] / [MC04 + MC148]*100 Counter description & details can be found in Appendix section or on click to respective counter in quicker way.


EDITION 1.2

‐

‐


5.2.2 ZTE SD CONG DESCRIPTION ZTE BSS system (ZXG10 V2.97) evaluates the SD CONG based on certain ‐

measurable counters from OMCR with below relation: SD CONG % = (C11625 C11626 + C11697) *100 / (C11625 + C11696) ‐

6. VENDOR WISE ROOT CAUSE ANALYSIS & OPTIMIZATION STEPS 6.1 TCH ASSIGNMENT SUCCESS RATE (TASR) 6.1.1 ALCATEL TASR ANALYSIS Alcatel (BSS 10 release) TASR analysis requires monitoring of the KPI from BBH report circulated from local\central MIS team on daily basis at cell level. It involves clear understanding of associated counter based internal system reports from NPO/OMC server as under which reflect the root causes for poor TASR % values and needs study of these reports in following sequence based on degradation severity: •

Active alarms report

•

Path balance report

•

RTCH Assignment report

•

Quality/Level report

•

Timing Advance (TA) report

•

Network parameter checks

Refer Appendix Sample Reports section for screenshot. Flow diagram for TASR improvement report checks: ‐

TASR CYCLE


EDITION 1.2

‐

‐


Active Alarms

Path Balance

RTCH Assign

Quality/Level

Timing advance

N/w parameter

Below Flowchart 1 represents the TASR% improvement cycle based on trigger condition and root causes: START

Identify & filter TASR % from BBH report for analysis

Check & clear active alarms

Yes

TASR % <98.75 %

Check for TRE Path bal. >5 dB

BSS problem, check Abis

without TMA

media stability with any CIC mismatch at Ater front (GTCNAAFLCPMR)

Verify the Tx/Rx path & rectify it

No

No further investigation reqd.


‐

EDITION 1.2

‐


MSC/BSC/Cell Parameters, Timers & Features audit for fine tuning purpose

Check failure phase in RTCH Assign report

Check BBH report for TASR % value after problem GTCNAFLRR

No

correction

>GTCNAFLBR Revisit the Yes

TASR %

improvement

>=98.75

cycle to START

Radio problem, check Quality/Level/TA RMS

Yes

reports with any TCH congestion (GTCNACGR)

STOP

Active Alarms

Path Balance

IOI

BER (U/L D/L) ‐

Timing advance

N/w parameter


‐

EDITION 1.2

‐





Yes

TASR % <98.75 %

Check RTFs Path loss <105


& >115 no TMA


Verify the Tx/Rx path & MSC/BSC/Cell

rectify it

Parameters, Timers & Features audit for fine tuning purpose Check IOI report for Uplink Intrf.

No

Check BBH report for TASR % value after problem correction

No



EDITION 1.2

‐

‐


Yes Revisit the TASR %

improvement

>=98.75

cycle to START

Radio problem, check Yes

Quality/Level/TA RMS reports with any TCH congestion (GTCNACGR)

STOP

6.1.2 ZTE TASR ANALYSIS ZTE (ZXG10 V2.97) TASR analysis requires monitoring of the KPI from BBH ‐

report circulated from local\central MIS team on daily basis at cell level. It involves clear understanding of associated counter based internal system reports from OMCR as under which reflect the root causes for poor TASR % values and needs study of these reports in following sequence based on degradation severity: •

Active alarms report

•

Path Balance report

•

Basic Measurement report

•

Timing Advance (TA) report

•

Network parameter checks

Refer Appendix Sample Reports section for screenshot. Flow diagram for TASR improvement report checks: ‐

TASR CYCLE

Active Alarms

Path Balance

IOI


EDITION 1.2

‐

‐


BER (U/L D/L) ‐

Timing advance

N/w parameter




Yes

TASR % <98.75 %

Check for TRE Path bal. >5 dB


without TMA


Verify the Tx/Rx path & rectify it

No



‐

EDITION 1.2

‐


MSC/BSC/Cell Parameters, Timers & Features audit for fine Check failure

tuning purpose

phase in RTCH Assign report Check BBH report for TASR % value after problem No

GTCNAFLRR

correction

>GTCNAFLBR Revisit the Yes

TASR %

improvement

>=98.75

cycle to START

Radio problem, check Quality/Level/TA RMS

Yes

reports with any TCH congestion (GTCNACGR)

STOP

6.2 SDCCH CONGESTION (SD CONG) 6.2.1 ALCATEL SD CONG ANALYSIS Alcatel (BSS 10 release) SD CONG analysis requires monitoring of the KPI from BBH report circulated from local\central MIS team on daily basis at cell level. It is highly critical to understand the radio network configuration & spatial location of cells based on which certain implications can be made for high SD Cong %.


EDITION 1.2

‐

‐


It is advised not to confuse with OMCR Counters & NPO Indicators in Alcatel (BSS 10 release). NPO Indicators can be direct OMCR Counters or Indirect Counters based on computation. Below Flowchart 4 represents the SD CONG% improvement cycle based on trigger condition and root causes: START

Identify & filter SD CONG % from BBH report for analysis

Check HW availability

No

SD CONG %! = 0.00

Yes


‐

EDITION 1.2

‐


STOP

7. APPENDIX 7.1 SDCCH DIMENSIONING SDCCH Dimensioning is the need for signaling resource optimization based on carried SDCCH & TCH traffic in a cell. Different vendors provide various solutions for dimensioning based on network settings & traffic requirements. Two methods available for SD dimensioning are: •

Automatic ( Load based increase/decrease of SDCCH/8)

•

Manual ( Traffic Estimations and Cell Statistics)

Automatic SD dimensioning is dependent on feature availability in the system although most of systems have dynamic SDCCH configuration feature to control SD traffic in peak hours. Dynamic SDCCH feature activation is network operator dependent & is highly recommended when flow monitoring of LAPD layer 2 messages is available. Manual SDCCH dimensioning is based on two following methods •

Traffic Estimations:

‐

Various Layer 3 events (LU/IMSI ATTACH DETACH/Call set ‐

‐

‐

up/SMS/FAX etc require average mean holding time (seconds) based on which SDCCH traffic estimation is done. This method is largely ignored in real networks due to varying probability of mean holding times of Layer 3 (MM/CM) messages and SD traffic estimation.


‐

EDITION 1.2

‐


•

Cell Statistics:

‐

Cell Statistics based SD dimensioning is highly recommended in current real time dynamic networks due to high demand for SDCCH resources and forms valid part of discussion in the manual. Cell statistic based approach considers maximum SDCCH channel occupancy in 24 hours or peak SD traffic for SD dimensioning as a critical input besides configured total SDCCH channels including (SDCCH/4, SDCCH/8) with or without CBCH. SD carried traffic or busy channels must be average of minimum 3 weeks to capture cell behavior on long term basis for effective dimensioning.

As a Thumb rule, Designed SDCCH Grade of Service (G.O.S) can be calculated as under: SDCCH G.O.S (%) = ¼* TCH G.O.S (%) GSM wireless networks consider TCH capacity dimensioning at 2 % G.O.S, hence SD capacity is dimensioned at 0.5% G.O.S. Common flowchart 5 for SD dimensioning based on cell statistic approach

is

as

under

and

same

Alcatel/Motorola/ZTE vendors as well. START

Check for Counter with max SD traffic or busy channels

SD

Yes

Dimensioning re d.

Max SD

Max SD busy

traffic

sub channels ‐

No

is

applicable

in


‐

EDITION 1.2

‐


No

No

Yes

Yes

Compute channels

Check for configured

frm carried SD traffic

& required SDCCH

using 0.5 % G.O.S

sub channel with

from Erlang B table

40% excess addition

‐

STOP Note: 8 SDCCH sub channels correspond to one hard coded SDCCH/8 ‐

7.1.1 ALCATEL SD DIMENSIONING METHOD Alcatel (B10 release) SD Dimensioning is done using NPO indicator GSDTRE which gives SD Erlang hourly basis for a day. Minimum 3 weeks data average with maximum SD Erlang observed in daily busy hour must be taken into account before further analysis. Refer steps as mentioned in Flowchart 5 for SD dimensioning.

7.1.2 ZTE SD DIMENSIONING METHOD ZTE (ZXG10 V2.97) ‐

SD Dimensioning is done using Basic

Measurement report.xls available in OMCR with counter C11627 (Maximum Number of Busy SDCCH). Minimum 3 weeks data average (If available) with maximum SD busy channels in 24 hours must be taken into account before further analysis.


EDITION 1.2

‐

‐


Refer steps as mentioned in Flowchart 5 for SD dimensioning.


EDITION 1.2

‐

‐


8. Optimization Process for other Radio KPIs SDCCH Drop Rate Definition: SDCCH Call Drop Rate indicates the probability of call drops that occur when MSs occupy SDCCHs. This KPI reflects the seizure condition of signaling channels. If the value of this KPI is high, user experience is adversely affected. SDCCH Call Drop Rate = Call Drops on SDCCH/ Successful SDCCH seizures Causes: 30. Due to Blind spot, low coverage level, or cross coverage. 31. High VSWR due to feeders leads to the reduction in the transmit power and in the receiver sensitivity. 32. Poor transmission quality and unstable transmission links over the Abis interface 33. Unavoidable inter network interference, interference from repeaters, or high and unavoidable intra network interference caused by aggressive frequency reuse Interference 34. unavailable terrestrial resources or faulty devices ‐

‐

Action: 1. Reduce Coverage hole, Blind spots by physically optimization. 2. By maintaining balance between Uplink Downlink path by achieving less VSWR value, proper tuning of RxLevAccessMin and RachLevAccessMin Parameter. 3. Stable Transmission – Minimum LapD failures 4. Proper Frequency plan to reduce Inference level by retuning frequency, Maio, HSN, reducing Overshooting. 5. Reshuffling of SDCCH Timeslot as per TRX efficiency. Rectification of Faulty TRX’s. 6. Timer T200 can be optimized as per transmission efficiency.


‐

EDITION 1.2

‐


Handover Success Rate Definition: The purpose of handover is to ensure the call continuity, improve the speech quality, and reduce the cross interference in the network, thus providing better services for the subscribers. Success ratio of handover is the ratio of the total number of successful handovers to the total number of handover requests. Success Rate of Handover = Successful Handovers/Handover Requests HSR is impacted due to 1. Blind spot, low coverage level, or cross coverage. 2. Unavoidable interference can be the inter network interference, interference from repeaters, or intra network interference resulting from aggressive frequency reuse. 3. Poor transmission quality and unstable transmission links over the Abis interface 4. Faulty devices, or asynchronous clocks 5. Imbalanced distribution of traffic volume in the network. If the network is congested badly, the handover failures increase because of no available TCHs and the handover success rate decreases. The network congestion does not affect the success rate of radio handover. Action st nd 1. Proper neighbor definition (1 tier mandatory and 2 tier definition as per requirement) 2. Maintaining proper footprint by physical optimization. 3. Reducing Interference level by smooth frequency plan 4. Stable error free transmission links 5. Avoiding Ping pong HO by defining proper HO margin parameter which may be due Level or Quality. 6. Providing appropriate time frame for clear msg or Establish msg between BTS’s by T8 timer 7. For intra Bsc HO, time to receives HO complete msg from BSC should be optimized by T3103 timer 8. Maximizing the HO cause due to Power budget. 9. Maintaining proper traffic distribution by physically, DR, queuing parameters to avoid HO failure due to neighbor cells congestion 10. Clock drift should be avoided. ‐

‐

‐


EDITION 1.2

‐

‐


TCH Call Drop Rate Call Drop Ratio on TCH indicates the ratio of the number of call drops to the number of successful TCH seizures after the BSC successfully assigns TCHs to MSs. TCH Call drops due to 1. Blind spot, low coverage level, or cross coverage. 2. Unavoidable interference can be the inter network interference, interference from repeaters, or intra network interference resulting from aggressive frequency reuse. 3. Poor transmission quality and unstable transmission links over the Abis interface 4. Faulty devices and high VSWR 5. If the target cell involved in the Directed Retry procedure is under another BSC 6. During intra Bsc handover 7. If preemption is used in MSC then lower priority MS will face call drop. ‐

‐

Action 1. Clean frequency plan viz. achieve minimum interference level by clean BCCH (CO/ADJ), MAL, MAIO, MS Plan. 2. Minimizing coverage holes by physical optimization (Orientation, Height, E.Tilt, M.Tilt). 3. Setting Radio link timeout parameter as per inter site distance viz. for rural sites RLT can be of higher value. 4. Similar for Rural site where uplink quality is poor, Rxlev Access min, Rach Access min parameter can be set appropriately. Proper balance should be maintained for this parameter else path imbalance will result and TCH drop will increase. TMA/TMB can be planned appropriately. 5. Minimize Ater Abis fluctuation – Link stability plays very vital role. 6. Ater Congestion further results in TCH call drops. Sufficient Ater argument should be maintained. 7. Power control used for HO should be properly designed to avoid drop where ever there is sudden RxLev drop. 8. During HO to neighbor cells should be having free TCH resources else call drop may increase. For this proper half rate thresholds should be defined as per traffic pattern, decongestion of these cells by capacity argument. 9. Queuing length should not made too long/short. 10. Drop due to intra Bsc HO, congestion free Ater argument should be maintained ‐


EDITION 1.2

‐

‐


11. Timer T305 and T308 interval should be well enough to receive the Disconnect and Release message from Msc and Bsc respectively. 12. Proper Neighbor definition should be maintained – some handovers cannot be performed and thus call drops. 13. By maximizing Power control HO’s reduces the interferences level, which further reduces TCH drop rate. 14. By DTX feature further Interference levels are reduced, reducing TCH drop.

RACH Success rate Def : Random Access Channel (RACH) is used by the MS on the “uplink” to request for allocation of an SDCCH. This request from the MS on the uplink could either be as a page response (MS being paged by the BSS in response to an incoming call) or due to user trying to access the network to establish a call.

RACH Failure can be due to : 1. AGCH Overload at Base Station 2. RACH Collisions 3. MS out of Range 4. Poor Uplink quality 5. BTS Receiver Problem ‐

Action 1. Appropriate no. of CCCH blocks should be designed as per Traffic pattern. Signaling link should be increased from 16k to 32k as per requirement to avoid overloading. 2. Minimum Coverage hole is first requirement for greater RACH success rate. 3. Use of DTX mode in Uplink reduces the interference level making less probability for RACH collision 4. Hardware alarm like difference in uplink and downlink path balance heavily impacts RACH success rate. H/W alarm should be minimized 5. Max. No Of Retransmission parameter allows the MS to retransmit again for AGCH by not incrementing the RACH access failure counter. 6. RACH Access min and RACH Busy Threshold parameter can be tuned to restrict the MS in out of range. If this parameter is set to a higher value, the actual coverage area of the network becomes small; if this parameter is set to a lower value; all drops are likely to


‐

EDITION 1.2

‐


occur because of invalid access or too weak access signals, thus decreasing the success rate. 7. Fluctuation in transmission media further decreases the success rate. Stable media need to be maintained. 8. Uplink quality can be further boosted by TMA/TMB.

Rx Quality Samples carried within 0 to 4 Level by sum of samples carried within 0 to 7 Levels, is termed as Rx Quality for the TRX/cell. Poor Speech Quality could be bad due to 1. Coverage holes 2. No Target cell for Handover 3. Interference • Co channel • Adjacent channel • External • Multipath • Noise 4. E1 fluctuation – poor FER 5. Path balance, VSWR , Hardware issue at BTS 6. Poor power budget thresholds 7. Half rate penetration 8. Repeater used – broadband/narrow/manual ‐

‐

Action 1. Both Uplink and Downlink good quality, proper uniform coverage patterns are prerequisite. 2. Clean frequency plan viz. achieve minimum interference level by clean BCCH (CO/ADJ), MAL, MAIO, MS Plan 3. Overshooting should be avoided by E/M tilt, height reduction and reorientation e.g. cells from high altitude (mountain) are tending to overshoot even with maximum tilt and height. Sector facing towards water (sea, pond) causes reflection and further interference in the surrounding. Proper orientation or isolated frequency plan need to be considered for these sites.

GSM KPI Optimization Appendix3

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